Like everything else left in the wake of the tragedy, it presented a mystery.

A day after Kazmierczak opened fire on a crowded Northern Illinois University classroom, investigators said they were no closer to understanding why.

Kazmierczak left a baffling trail of mixed messages. He was bright and earnest, if sometimes shy, and had dedicated his professional life to criminal justice and helping people.

But on Thursday, he slaughtered four defenseless young women and a young man in a barrage of gunfire.

His rampage was apparently premeditated. At his Champaign apartment, his former girlfriend, with whom he still lived, had received packages of gun accessories with instructions from Kazmierczak that she should not open them until Valentine's Day, law enforcement sources said.

But professors at NIU and at the University of Illinois said they saw a young man looking forward to his future.

In a Jan. 22 e-mail to his academic mentor, Kazmierczak said he was thinking about law school but felt he needed to retake the qualifying exam. He also was newly interested in a branch of sociological research, said NIU professor emeritus Jim Thomas.

"Everything is going well at UIUC, as I am just starting my third semester here, and am about half-way done with the academic portion (the internship portion is the final semester)," Kazmierczak wrote to Thomas in his most recent e-mail.

Kazmierczak went on to muse about his long-term aspirations.

"I really believe in the cliche now that the further I go in college, the less I realize I know about a multitude of subjects," he wrote. "All I know is I want to work in the [criminal justice system] in some capacity; as a social worker or as an overly litigious advocate of prisoners."

People who knew him in academic circles said his recent demeanor completely lacked any warning signs of a troubled soul.

Kazmierczak was enrolled in the University of Illinois' school of social work master's degree program, where Jan Carter-Black was his academic adviser. Although she had not seen him this semester, she met regularly with him and taught him in the fall semester in a course titled Human Behavior in the Social Environment.

"He was engaging, he was participative, his attendance was good," she said. "He projected a commitment to study and he was a good student. ... I saw Steven as a very respectful student. In our interactions, he was very conscientious of my time. If we had 45 minutes to meet, he would come prepared to have real discussions."

Thomas said he was dumbfounded when the news of the gunman's identity emerged from the campus Thursday.

"When I heard yesterday that it was a student in corrections and social justice, former grad student, I thought, 'Oh my God, that's Steve. That has to be Steve,'" he said. "It's nuts, nuts, totally nuts. He was the most gentle, even guy."

Investigators were trying to determine where Kazmierczak's path diverged into madness. Acquaintances said they were very surprised to learn he owned guns. But authorities said he had purchased six weapons since August, and they believed he owned a few more that they have not yet recovered.

Armed with a shotgun and three semiautomatic handguns, Kazmierczak entered the lecture hall Thursday and opened fire without uttering a word. He killed five students and wounded 16 others before taking his own life.

Authorities were puzzled when they came across the glued-shut duffel bag in his hotel room, and they called in a bomb squad, suspecting Kazmierczak had booby-trapped the luggage. Instead, they found the bag stuffed with ammunition for the guns he carried into the lecture hall, according to law enforcement sources.

Family members declined to talk about him, putting out a brief written statement late Friday and asking for privacy.

Kazmierczak grew up in Elk Grove Village with his parents and a sister who is a year older and lives in Urbana. Kazmierczak's parents sold their house and moved to Florida. His mother died in 2006, public records say.

He was a B-student and 1998 graduate of Elk Grove High School, was a member of the school band, and participated in the Japanese language program and a public service class, according to a spokeswoman for the school.

Matt Fahrenbacher played in the school band with Kazmierczak, whom he called a "decent saxophone player," who often wore black clothing but seemed normal.

Kazmierczak never seemed like a loner, said Fahrenbacher, now a math teacher at Niles North High School in Skokie. "I always thought there was a little undercurrent of not getting along with teachers."

Ryan Chapetta also played in the band and recalled Kazmierczak as a "sweet, gentle, soft-spoken person," she said.